Legal Question in Civil Litigation in California

There's no legal requirement for it at all. It's completely a style issue.

No. For me, I use a background section if I feel the judge or research attorney needs to know something before readng the rest of the brief.

The reason you are being advised to get a lawyer is that your question shows you so completly misunderstand legal practice and proceedure that you don't even know the difference between a complaint and a memorandum of points and authorities, sometimes called a "brief." There is no such thing as a Background section OR a Statement of Facts in a complaint in California (or anywhere else I've ever seen). Those are sections of a legal "MPAA" or "brief" which is an entirely different thing from a complaint. If you don't even understand the difference between briefs and complaints, the only thing you will get from representing yourself is a thorough beating in every step of the case.

I agree with Mr McCormick. You may be over your head. Comparing federal complaints to California complaints is comparing apples and oranges. California is a fact pleading jurisdiction where the Feds are a notice pleading jurisdiction. If you don't do the the facts right your case will not even survive demurrer. If you survive demurrer you will need the need to figure out conferences, discovery, and a whole bunch of time frames that you may be unfamiliar with.

Law is like medicine, you may be able to do first aid on your slf and self diagnose and treat minor illness but you would never do surgery on your self and this is no different.

I have never seen a complaint where a "background" section added anything, and think I have done them only when a more senior lawyer in my firm requested one. Note that the "background" section is different than a "jurisdictional" section often required in federal court.

Having said that, you still need to plead all the essential facts in your complaint. Leave any essential fact out, and you risk a demurrer.